refactor: use the SDK blockchain client

[TaprootFreak]

Consumer side of step 5 of DFXswiss/packages#198: use the blockchain client from @dfx.swiss/react
instead of a local useApi() wrapper.

Depends on DFXswiss/packages#203.

Changes

Both local hooks stay — what changes is what they call. The HTTP layer and the request/response types
now come from the package; the chain-specific parts stay here, which is exactly the split the package
side was built for:

• blockchain-balance.hook.ts keeps the join against the asset list (the API answers with asset ids)
  and drops its local BalanceDto / GetBalancesResponse.
• blockchain-transaction.hook.ts keeps the Solana base64 deserialization and the Tron JSON parsing
  and drops its local UnsignedTransactionDto / BroadcastResultDto.

No call site of either hook changes.

Before this can go green

The package pin in package.json still points at the published @dfx.swiss/react, which does not
export useBlockchain yet. CI stays red until DFXswiss/packages#203 is merged and published and
the pin is raised here. Verified locally against a build of that branch: tsc clean,
npm run lint clean, full suite at 673 passing with no new failures (the two suites failing on
develop today still fail, unchanged).

[github-actions]

🤖 PR Review Bot

❌ TypeScript: 4 errors

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